Variable focus stereoscopic display system and method

ABSTRACT

A variable focus stereoscopic display system includes first and second lenses positioned between a viewer&#39;s eyes and a stereoscopic display that alters the distance to the focus plane of the viewer based on the vergence of the viewer&#39;s eyes while viewing the stereoscopic display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. patent application Ser. No. 13/077,197,filed Mar. 31, 2011.

TECHNICAL FIELD

The exemplary embodiments described herein generally relate toinformation displays and more particularly to stereoscopic displays.

BACKGROUND

Three dimensional (3D) displays are becoming increasingly popular.Presently, many 3D displays implement stereoscopic techniques togenerate a 3D visual display to a user. Such displays, which may bereferred to as stereoscopic 3D displays, rely on the well knownstereoscopic imaging technique for creating the illusion of depth in animage. As is generally known, stereoscopy is a method of creating a 3Dimage from a pair of two dimensional (2D) images, in which each of the2D images preferably represents the same object or image from a slightlydifferent perspective, such as a right eye perspective and a left eyeperspective.

Referring to FIG. 1, a typical prior art stereoscopic display 102 isconfigured to generate a 3D representation of an image viewable by aviewer 104. A left eye 106 and a right eye 108 of the viewer 104 arefocused on a focus plane 109 at the stereoscopic display 102 (the viewer104 is a binocular viewer having two eyes separated by an interpupillarydistance 110). A left stereo channel selection mechanism 112 ispositioned between the left eye 106 and the stereoscopic display 102 anda right stereo channel selection mechanism 114 is positioned between theright eye 108 and the stereoscopic display 102. Two stereo perspectiveviews, a left perspective view 116 and a right perspective view 118, ofa single stereoscopic object or feature 120 are presented to thebinocular viewer with a convergence plane 122 (perceived location) basedon vergence. The distance between the focus plane 109 and theconvergence plane 122 is a depth cue disparity 121. Stereo channelselection mechanisms 112 and 114 can take many conventional forms wellknown in the art, including polarized filters, colored filters, temporalshutters, and others. These selection mechanisms 112, 114 can also beincorporated as part of the display, for example using lenticular arraysor other mechanisms known in the art. The function of the stereoselection mechanisms 112, 114 is to cause the left eye 106 to see onlyleft perspective view 116 and right eye 108 to see only rightperspective view 118. When the viewer's gaze is directed at feature 120,the perceived depth, or distance from the viewer, of feature 120 isdetermined by the intersection or converging of the lines of sight fromthe eyes to their respective perspective views.

Stereoscopic display systems, which provide enhanced interpretation ofthe information by users over two dimensional displays and can result inimprovements in performing various tasks as well as various otherpotential benefits, may be used for applications which rely on periodsof extended concentration and/or critical information, such as avionics,medical, engineering/industrial or military applications, and may alsobe used for applications of shorter concentration periods, such asentertainment applications, for example, movies. Stereoscopic 3Ddisplays have been conventionally directed toward intermittent andnon-critical applications such as entertainment and modeling. One of thelingering concerns of use for extended periods or critical informationis the human tolerance for the vergence-accommodation disparity presentin these displays. Vergence refers generally to the relative inwardangle of the two eyes to detect depth, whereas accommodation refers tothe distance for which the eyes are optically focused. Under normalreal-world circumstances of viewing actual objects (including most twodimensional electronic displays), the vergence and accommodation cuestypically match. Both of these cues are valid 3D depth or distance cues,along with a number of other 3D cues, for example, motion parallax,occlusion, relative size, absolute size, linear perspective, andshading/shadows. Conventional stereoscopic displays achieve thesensation of 3D by manipulating vergence cues while having the eyesremain focused on a fixed display surface or screen. This disparitybetween competing depth cues can result in viewer fatigue anddiscomfort, especially over an extended period of time, and canpotentially interfere with the benefits of using a stereoscopic display.The potential for fatigue, including eyestrain, headaches or otherdiscomfort, is generally believed to be increased as the degree ofmismatch increases and can potentially interfere with the benefits ofusing a stereoscopic display.

As the environment, such as aviation, in which these stereoscopicsystems are used becomes more complex, it is preferable that theoperator be attentive and receive information in a timely manner andwith little stress (such as eye fatigue) to ensure proper operation. Theuser must interpret the information provided on the screen occupyinghis/her thought processes when he/she may have many other decisions tomake.

Accordingly, it is desirable to provide a method and system displayinginformation stereoscopically that may be more easily understood by theuser without taxing human tolerances. Furthermore, other desirablefeatures and characteristics of the exemplary embodiments will becomeapparent from the subsequent detailed description and the appendedclaims, taken in conjunction with the accompanying drawings and theforegoing technical field and background.

BRIEF SUMMARY

Apparatus' and methods alter the distance to the focus plane of thestereoscopic 3D display based on the vergence of the eyes while viewingportions of the display. Embodiments include both active and passivemethods.

In a first exemplary embodiment, a variable focus stereoscopic displaysystem defining a focus plane, the variable focus stereoscopic displaysystem comprising a first lens configured to be positioned between afirst eye and a stereoscopic display, and a second lens configured to bepositioned between a second eye and the stereoscopic display, whereinthe first and second lenses are configured to modify the distance of thefocus plane from the first and second eyes in response to a vergence ofthe first and second eyes, and changes in the focus distance arepositively correlated with changes in the convergence distance of thelines of sight of the first and second eyes.

Another variable focus stereoscopic display comprises a focus plane, afirst lens configured to be positioned over a first eye for viewing thestereoscopic display, a second lens configured to be positioned over asecond eye for viewing the stereoscopic display, the first and secondlenses each comprising a first portion having a first optical power, anda second portion having a second optical power higher than the firstoptical power, the first and second portions configured to increase thefocus distance as the convergence distance increases (corresponding todecreased convergence), and to decrease the focus distance as theconvergence distance decreases (corresponding to increased convergence).

A method for adjusting a focus plane for viewing a stereoscopic display,comprising altering the distance of the focus plane from first andsecond eyes in response to vergence of the first and second eyes,wherein changes in the focus plane distance are positively correlatedwith changes in the convergence distance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a prior art schematic of two eyes viewing a displayed featureon a stereoscopic display;

FIG. 2 is a schematic of two eyes viewing a displayed feature on astereoscopic display having a first shifted focus plane in accordancewith an exemplary embodiment;

FIG. 3 is a schematic of two eyes viewing a displayed feature on astereoscopic display having a second shifted focus plane in accordancewith an exemplary embodiment;

FIG. 4 is a functional block diagram of a system in accordance with theexemplary embodiment of FIG. 2;

FIG. 5 is a flow chart of the method for implementing the exemplaryembodiments;

FIG. 6 is a near-to-eye stereoscopic display system in accordance withan exemplary embodiment;

FIG. 7 is a functional block diagram of a aircraft display system inwhich the exemplary embodiments may be used;

FIG. 8 is a schematic of two eyes viewing a displayed feature on astereoscopic display having a shifted focus plane in accordance withanother exemplary embodiment;

FIG. 9 is a first pair of lenses for implementing the exemplaryembodiment of FIG. 8; and

FIG. 10 is a second pair of lenses for implementing the exemplaryembodiment of FIG. 8.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. Any implementation describedherein as exemplary is not necessarily to be construed as preferred oradvantageous over other implementations. Furthermore, there is nointention to be bound by any expressed or implied theory presented inthe preceding technical field, background, brief summary, or thefollowing detailed description.

A stereoscopic display system (three dimensional (3D)) provides twoimages of the same object taken from two perspectives that when viewedby two eyes are interpreted as an image having depth (depth perception).The stereoscopic display system described herein provides enhancedusability by users of the display, especially for applications whichrely on extended duration and/or critical information, such as avionics,medical, engineering/industrial, or military applications.Entertainment-based applications would also benefit from theseimprovements even though the user has an increased opportunity to divertattention from the stereoscopic content and thereby reduce a strain onhuman tolerance.

The exemplary embodiments described herein alter the distance to thefocus plane of the stereoscopic 3D display based on the vergence of theeyes while viewing portions of the display. Embodiments include bothactive and passive methods.

The following definitions apply as used herein. Convergence meanscentral or foveal binocular lines of sight rotated inward and crossingat a point in front of the viewer. Increased and decreased convergencecorresponds to the crossing point being closer to or further from theviewer, respectively. Substantially zero convergence corresponds to thecrossing point being very distant, e.g., infinity, from the viewer.Divergence refers to the lines of sight diverging (moving apart) fromzero convergence in front of the viewer, which is not normally the casefor human viewers. Vergence describes the relationship of convergence todivergence. Focus distance is the distance from the eye to the effectiveapparent plane of focus as seen by the eye. Convergence distance is thedistance from the eye to the convergence crossing point.

A first embodiment involves the use of dynamic focus lenses over eacheye. These lenses are preferably electro-optically adjustable, forexample through the use of switchable liquid crystal materials,electro-active polymer gels, field deformable surfaces or otheroptically switchable materials.

The drive signal for the lens pair is to be derived from a correspondingdifferential eye tracking sensor mechanism, such as one or more smallsensors (cameras) which would detect the relative orientation orvergence of the two eyes. In one example, as the two eyes converge to abinocular representation of a particular object or feature in thestereoscopic image, the sensor would detect the apparent stereo distancefrom the eyes and would add or subtract optical power to the lenses tomake the apparent focus distance of the object or feature match theconvergence distance based on vergence cues. The variable focus lenseswould preferably be adjusted to a more positive (or less negative) powerto effectively increase the apparent focus distance when vergence cuesindicate greater distance or depth. For showing an object at infinity, apreferred (but non-limiting) positive focal length for the lenses wouldbe the distance from the lenses to the stereoscopic display screen orpanel. For apparent depths close to the viewer and in front of thedisplay, the lenses would preferably impart a somewhat negative (or lesspositive) optical power such that the eyes, including normally worncorrective eyewear or contact lenses, would have to focus closer to seea sharp image. In this manner, relative changes in the one depth cue,the focus distance, are positively correlated with relative changes inanother depth cue, the convergence distance.

While full compensation of the accommodation distance might completelyremove visual fatigue, partial compensation may be sufficient. Visualfatigue from depth cue mismatches is difficult to quantify, andpropensity for fatigue may vary significantly from person to person.

A passive variable focus embodiment includes a suitable pair ofprogressive focus lenses. In typical bifocal or progressive lenses forreading or other close up work, the optical power of the lens mosttypically increases from top to bottom of the lens. In this embodiment,however, the optical power of the lens increases from the inner edge(converged lines of sight suggesting slight negative power in thevariable focus lens) and reaching zero or preferably higher power towardthe centers and outer regions of the progressive lenses.

Yet another embodiment is a variant on the passive progressive lensapproach which applies a correction while allowing somewhat more usercontrol based on viewer head position. As in previous embodiments, thereis a vergence-dependency of the optical power, but this is combined withan up/down tilt aspect.

A further option is to combine these active and passive techniques toreduce the degree of actively switched optical power needed and at thesame time relax the need to center the foveal view relative to thepassive eyewear. Similarly, both active and passive methods can be usedto restrict the variable power to the viewing of the particular display,while avoiding the variable power when looking away from the display.Numerous other similar techniques and/or apparatus are possible.

While described in the context of a standard display, such as anactive-matrix liquid crystal display, plasma, organic light emittingdiode, projection, or other real image display, similar techniques canbe used with a collimated display, such as a head up display orbinocular near-to-eye display, which provides vergence cues.

The system/approach as described applies the disclosed techniques toexpand the range of accommodation or focus distance required of theviewer's eyes, so that instead of simply focusing on the plane of astereoscopic display, the eyes focus over a larger and more naturalrange for the imagery being viewed. Another candidate usage for theabove described techniques is to instead shrink the range ofaccommodation or focus distance required from the viewer's eyes whenviewing a real world or other volumetric scene. This would be analogousto using conventional progressive or bifocal eyewear, except that theeffective lens prescription being utilized would be controlled, eitheractively or through a combination of both active and passive techniques,based on actual eye vergence rather than tilting of the head. In thiscase, the progression of the optical power would preferably be reversedfrom the stereoscopic embodiments.

The lenses described in the various embodiments may be implemented inany one of several arrangements, for example, binoculars, or embedded ina hardware system in which the viewer would move his eyes to the lensesor otherwise appropriate vantage point; however, the preferredembodiments are implemented in a head-worn system as describedhereinafter. Additionally, the display may alternatively be included inthe head worn system. Though the methods and systems may be implementedin any one of several environments, for example, medicine, modeling, andmobile vehicle such as automobiles, ships, and heavy machinery, the usein an aircraft system is described as an example.

Techniques and technologies may be described herein in terms offunctional and/or logical block components, and with reference tosymbolic representations of operations, processing tasks, and functionsthat may be performed by various computing components or devices. Suchoperations, tasks, and functions may be referred to as beingcomputer-executed, computerized, software-implemented, orcomputer-implemented. In practice, one or more processor devices cancarry out the described operations, tasks, and functions by manipulatingelectrical signals representing data bits at memory locations in thesystem memory, as well as other processing of signals. The memorylocations where data bits are maintained are physical locations thathave particular electrical, magnetic, optical, or organic propertiescorresponding to the data bits. It should be appreciated that thevarious block components shown in the figures may be realized by anynumber of hardware, software, and/or firmware components configured toperform the specified functions. For example, an embodiment of a systemor a component may employ various integrated circuit components, e.g.,memory elements, digital signal processing elements, logic elements,look-up tables, or the like, which may carry out a variety of functionsunder the control of one or more microprocessors or other controldevices.

For the sake of brevity, conventional techniques related to graphics andimage processing, navigation, flight planning, aircraft controls, andother functional aspects of certain systems and subsystems (and theindividual operating components thereof) may not be described in detailherein. Furthermore, the connecting lines shown in the various figurescontained herein are intended to represent exemplary functionalrelationships and/or physical couplings between the various elements. Itshould be noted that many alternative or additional functionalrelationships or physical connections may be present in an embodiment ofthe subject matter.

Referring to FIG. 2 and in accordance with an exemplary embodiment, likeelements in FIG. 2 are identified with like reference numerals of thosein FIG. 1. The stereoscopic display 102 may be implemented using any oneof numerous suitable stereoscopic display devices now known or developedin the future. The stereoscopic display 102 may also be implementedusing either coplanar display media or non-coplanar display media. Asensor 222 is positioned with respect to the eyes 106, 108 of the viewer104 for determining the amount, or degree, of vergence, typicallyconvergence which is an inward viewing angle, of the eyes towards oneanother. The sensor 222 could take any form capable of detecting therelative directions the two eyes 106, 108 are aimed, and may be mountedalong with the lenses 212, 214 and any other optical components requiredsuch as polarizers, shutters, selective filters and/or correctiveeyewear. The sensor 222 could sense vergence via analysis of sensorimagery, or alternately could sense vergence by mechanical, electricalor any other means possible. The lens 212 is positioned between the lefteye 106 and the stereoscopic display 102 and the lens 214 is positionedbetween the right eye 108 and the stereoscopic display 102. These lenses212, 214 are preferably electro-optically adjustable, for examplethrough the use of switchable liquid crystal materials, electro-activepolymer gels, field deformable surfaces or other optically switchablematerials. See for example, the technology described in U.S. Pat. Nos.4,190,330 or 6,619,799. Dynamically adjusted contact lenses would beanother embodiment. Alternately, the lenses could be mounted separatelyfrom the head of the viewer. A single lens or lens region could be usedprovided both lines of sight pass through it. Other dynamic focus meanswould also be possible, such as optics moved or deformed by mechanicalmeans, or switchable viewing screen depths. Modifying the focus of thelens or lens system in this context refers to modifying the opticalpower, and thereby the related focus distance for the display. It shouldbe noted that the focus distance is adjusted based on vergence of theeyes, not the input image data to the stereoscopic display.

FIG. 4 depicts a block diagram of a system 400 in accordance with thepresent embodiments. A processor 420 is coupled to the lenses 212, 214and is configured to receive information from the sensor 222 regardingthe degree of vergence and, in response thereto, adjust the strength ofthe lenses 212, 214 to alter the focal point or focal length. Forexample, when the sensor 222 determines the eyes have rotated outward(away from one another, such that they are less converged), the lenses212, 214 are adjusted to shift the required focus of the eyes 106, 108the distance (focus plane shift) 224 (FIG. 2) from the display screen102 (where the eyes are focused without adjustment) to a focus plane 226(FIG. 2) further from the eyes 106, 108 (the maximum line of sight wouldbe infinity). Alternatively, if the sensor 222 senses the eyes haveturned more inward (FIG. 3) towards one another (more converged), thelenses 212, 214 are adjusted to shift the corresponding focus of theeyes 106, 108 to a convergence plane 332 closer to the eyes 106, 108.

This method (FIG. 5) of adjusting the visual focus for viewing astereoscopic display includes the step of altering the focus planedistance between a stereoscopic display focus plane and first and secondeyes of a viewer in response to vergence of the first and second eyes,wherein changes in the focus plane distance are positively correlatedwith changes in the convergence distance for the first and second eyes'lines of sight.

The adjustment of the visual focus for a stereoscopic display may beaccomplished in several types of systems, for example, the vergencesensor 222 and the lenses 212, 214 may be positioned on a stationaryapparatus, with the user positioning himself to view a display throughthe lenses 212, 214, or they may be positioned on a head-worn visionsystem 632 (FIG. 6). The lens system 632 is a type of head worn lenssystem which uses a visor, a helmet, goggles or a cap to place thelenses 212, 214 and optionally also the channel selection mechanisms112, 114 in front of both eyes 106, 108 of the viewer 104. As shown, aheadband 634 positions the lens 212, 214 over the eyes 106, 108.Typically, the variable focus lenses are a material (such as a liquidcrystal materials, electro-active polymer gels, field deformablesurfaces, or other optically switchable materials) so that the focus ofthe lenses may be adjusted in a manner known to those in the industry(see U.S. Pat. Nos. 4,190,330 and 6,619,799). In this embodiment,sensors 222 are positioned on the headband 634 so they may detectmovement of the eyes. While four sensors 222 are shown in FIG. 6, anynumber from one or more may be used, and other components and processingalgorithms may be applied. In some applications it may be desirable tocalibrate the variable focus lens system such that the optical powerprovided by the lenses is substantially zero at a viewer-preferred focusplane, for example when the vergence of the eyes is consistent withviewing the physical display device. Another example could be to adjustthe zero power plane such that both near and distant stereoscopicdistances are comfortable for the viewer.

Head-worn vision system 632 may also comprise one or more light emittingdiodes (LED), not shown, which may be placed along with sensors 222, toenable monitoring the head position of operator 104 by monitoring theposition and orientation of the head-worn vision system 632. In thismanner, the operator's direction and location of gaze at any point intime can be sensed for enabling the dynamic lenses 212, 214 when theoperator 104 is viewing the stereoscopic 3D display or disable thedynamic lenses 212, 214 when the operator 104 is not viewing thestereoscopic 3D display. The LEDs are preferably infrared in order toemit wavelengths not visible to the operator 109 and thereby notinterfere with, e.g., operation of an aircraft and/or the view of theoperator 109. The present embodiment, however, is not limited to the useof infrared LEDs or, in fact, is not limited to the use of LEDs, and mayinclude any reflective surface or emissive device attachable to thehead-worn vision system 632 that would allow sensing of the position andorientation of the head-worn vision system 632 and, consequently,determination of the direction of gaze or focus of the pilot. The sensor(not shown) for sensing the emissions from the LEDs on the head-wornvision system 632 may be positioned on a stationary nearby object. Otherhead-tracking configurations may also be used. In one other exemplaryembodiment, one or more (but not all) of sensors 222 face forward tocollect imagery of the forward scene. The forward scene is then analyzedin conjunction with the binocular gaze angles and focus plane distancedetected as described above to determine the spatial location ofbinocular foveal interest.

In another embodiment, this detected location of interest is used todetermine whether the operator is looking at the 3D display or not. Thisinformation is then used to enable or disable the variable focus 3Ddisplay functionality. One mode of operation when the 3D display contentis not being viewed foveally is to switch the variable focus back to anominal optical power setting. The preferred optical power setting inthis case is zero optical power, but other nominal power settings can beused. In yet another embodiment, the optical power of the variable focuseyewear continues to be adjusted based on vergence, but the opticalpower is actively increased as the convergence distance is decreasedover a certain range when not viewing the 3D display or when no 3Ddisplay is present. This is analogous to providing reading glasses whichautomatically adjust their optical power based on convergence of theeyes. It is important to note that changes, if any, in response toconvergence distance in this non-3D mode are generally in the oppositedirection of those provided when viewing the 3D display, in other wordsoptical power is increased rather than decreased as the convergencedistance is decreased.

As previously mentioned, many applications exist for the use of thevariable focus stereoscopic display system and method described herein.Such a display system would be especially of benefit in an avionicsenvironment such as a flight deck display system 700 (FIG. 7) includinga user interface 702, a processor 704, one or more terrain databases 706(including runway and taxiway information), one or more navigationdatabases 708, sensors 712, external data sources 714, one or moredisplay devices 716 including the stereoscopic display (FIG. 2), and thevariable focus lens system 717 previously discussed. The user interface702 is in operable communication with the processor 704 and isconfigured to receive input from a user 709 (e.g., a pilot) and, inresponse to the user input, supplies command signals to the processor704. The user interface 702 may be any one, or combination, of variousknown user interface devices including, but not limited to, one or morebuttons, switches, knobs, and touch panels (not shown).

The processor 704 may be implemented or realized with a general purposeprocessor, a content addressable memory, a digital signal processor, anapplication specific integrated circuit, a field programmable gatearray, any suitable programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationdesigned to perform the functions described herein. A processor devicemay be realized as a microprocessor, a controller, a microcontroller, ora state machine. Moreover, a processor device may be implemented as acombination of computing devices, e.g., a combination of a digitalsignal processor and a microprocessor, a plurality of microprocessors,one or more microprocessors in conjunction with a digital signalprocessor core, or any other such configuration. In the depictedembodiment, the processor 704 includes on-board RAM (random accessmemory) 703, and on-board ROM (read-only memory) 705. The programinstructions that control the processor 704 may be stored in either orboth the RAM 703 and the ROM 705. For example, the operating systemsoftware may be stored in the ROM 705, whereas various operating modesoftware routines and various operational parameters may be stored inthe RAM 703. The software executing the exemplary embodiment is storedin either the ROM 705 or the RAM 703. It will be appreciated that thisis merely exemplary of one scheme for storing operating system softwareand software routines, and that various other storage schemes may beimplemented.

The memory 703, 705 may be realized as RAM memory, flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. In thisregard, the memory 703, 705 can be coupled to the processor 704 suchthat the processor 704 can be read information from, and writeinformation to, the memory 703, 705. In the alternative, the memory 703,705 may be integral to the processor 704. As an example, the processor704 and the memory 703, 705 may reside in an ASIC. In practice, afunctional or logical module/component of the display system 700 mightbe realized using program code that is maintained in the memory 703,705. For example, the memory 703, 705 can be used to store data utilizedto support the operation of the display system 700, as will becomeapparent from the following description.

No matter how the processor 704 is specifically implemented, it is inoperable communication with the terrain databases 706, the navigationdatabases 708, and the display devices 716, and is coupled to receivevarious types of inertial data from the sensors 712, and various otheravionics-related data from the external data sources 714. The processor704 is configured, in response to the inertial data and theavionics-related data, to selectively retrieve terrain data from one ormore of the terrain databases 706 and navigation data from one or moreof the navigation databases 708, and to supply appropriate displaycommands to the display devices 716. The display devices 716, inresponse to the display commands, selectively render various types oftextual, graphic, and/or iconic information.

The terrain databases 706 include various types of data representativeof the taxiways and runways over which the aircraft is taxing, and thenavigation databases 708 include various types of navigation-relateddata. The sensors 712 may be implemented using various types of inertialsensors, systems, and or subsystems, now known or developed in thefuture, for supplying various types of inertial data, for example,representative of the state of the aircraft including aircraft speed,heading, altitude, and attitude. In at least one described embodiment,the sensors 712 include an Infrared camera. The other avionics receivers718 include, for example, an ILS receiver and a GPS receiver. The ILSreceiver provides aircraft with horizontal (or localizer) and vertical(or glide slope) guidance just before and during landing and, at certainfixed points, indicates the distance to the reference point of landingon a particular runway. The ILS receiver may also give ground position.The GPS receiver is a multi-channel receiver, with each channel tuned toreceive one or more of the GPS broadcast signals transmitted by theconstellation of GPS satellites (not illustrated) orbiting the earth.

The display devices 716, as noted above, in response to display commandssupplied from the processor 704, selectively render various textual,graphic, and/or iconic information, and thereby supplies visual feedbackto the user 709. It will be appreciated that some of the display devices716 may be implemented using any one of numerous known display devicessuitable for rendering textual, graphic, and/or iconic information in aformat viewable by the user 709. Non-limiting examples of such displaydevices include various flat panel displays such as various types of LCD(liquid crystal display), TFT (thin film transistor) displays, andprojection display LCD light engines. The display devices 716 mayadditionally be implemented as a panel mounted display, or any one ofnumerous known technologies. One or more of the display devices may be astereoscopic 3D display as described herein.

The display devices 716 may additionally be implemented as a panelmounted display, a HUD (head-up display) projection, or any one ofnumerous known technologies. It is additionally noted that the displaydevices 716 may be configured as any one of numerous types of aircraftflight deck displays. For example, it may be configured as amulti-function display, a horizontal situation indicator, a verticalsituation indicator, or a primary flight display.

The variable focus stereoscopic display system 717 preferably includes avariable focus lens system 632. The preferred exemplary embodiment alsoincludes the operator 709 of a vehicle, such as a flight crew member ofan aircraft, wearing a variable focus lens system 632.

Referring to FIG. 8, the first exemplary passive variable focusembodiment includes the lens 812 positioned between the left eye 106 andthe stereoscopic display 102, and the lens 814 positioned between theright eye 108 and the stereoscopic display 102. A frontal view of thelenses 812, 814 is shown in FIG. 9. An inner portion 942 of each of thelenses 812, 814 (adjacent to one another) is constructed with a lower(e.g., negative) optical power than a center portion 944 and optionallyan outer portion as well. Therefore, as the stereoscopic binoculardisparity causes the viewer 104 to look more inward through the portions942, the lower optical power causes the effective focus plane to adjustcloser to the viewer 104 from the physical focus plane 109 of thestereoscopic display 102. Conversely, as the three dimensional viewcauses the viewer 104 to look less inward and more forward, with reducedconvergence, through the portions 944, the higher optical power causesthe effective focus plane to adjust further from the viewer 104, forexample from the physical focus plane 109 of the stereoscopic display102 to the vergence-related convergence plane 826 (FIG. 8). Theprogression between regions of differing optical power can for examplevary smoothly or via one or more discrete steps.

The degree of focus compensation to be used may vary with the intendedusage or individual preferences. This is true for both passive andactive embodiments, as well as combinations of passive and activevariable focus techniques wherein the stereoscopic 3D system wouldinclude both the dynamic and passive focus lenses. Some viewers may dobest with a strong progressive variation, while others may prefer lesscompensation. This might be based on many factors, including but notlimited to the presence of age-related presbyopia, details of theintended application, or level of prior experience with stereoscopic 3Ddisplays (and perhaps a correspondingly higher tolerance of thevergence-accommodation mismatch). The vergence-dependent correction canbe combined with appropriate individual optics or prescription and/orstereoscopic selection optics, as desired. In the passive eyewearexample, best compensation will be achieved when the head (and not justthe eyes) is aimed toward the displayed object or feature of interest,for extended viewing of specific features in the displayed image. Someadditional benefit may possibly be obtained by extending the distancefrom the eyes to the lenses, thereby spreading the progressive poweracross a larger portion of the lens area. In one exemplary embodiment,the lenses are positioned 50 mm or more from the eyes.

A second exemplary passive variable focus embodiment (FIG. 10) includesthe lens 1012 positioned between the left eye 106 and the stereoscopicdisplay 102, and the lens 1014 positioned between the right eye 108 andthe stereoscopic display 102. A lower inner portion 1042 of each of thelenses 1012, 1014 is constructed with a lower (more negative or lesspositive) optical power than an upper center and outer portion 1044.Therefore, when the viewer 104 shifts his vision down and inward throughthe portions 1042, the lower optical power causes the focus plane toadjust closer (not shown) to the viewer 104 from the physical focusplane 109 of the stereoscopic display 102. Conversely, as the viewer 104shifts his view more outward and up through the portions 1044, thehigher optical power causes the focus plane to adjust further from theviewer 104 from the focus plane 109 of the stereoscopic display 102 tothe perceived depth or convergence plane 826 (FIG. 8). In a mannersimilar to the use of traditional bifocal or progressive lens eyewear,the wearer can adjust the orientation to maximize the viewing comfortfor the object or feature of interest by moving his head, and thereforethe lenses, up or down. Due to the inclusion of the user repositioning,this variant may be best suited for applications which involvefamiliarity of use and deliberate emphasis on detail in particularportions of the stereoscopic space, such as remote manipulation,monitoring, modeling or analysis. This approach may be less suitable forapplications such as entertainment where the region of emphasis is lesspredictable. The variation of optical power is largely inverted relativeto traditional bifocal progression, but is still consistent with viewingnear objects through the lower portion and more distant stereoscopicobjects through the central or upper portions. Other arrangements cancertainly be substituted.

In summary, several exemplary embodiments have been described, includingboth active and passive devices, of a variable focus stereoscopicdisplay apparatus for varying the focus in response to changing vergenceof the viewer. Active devices include adjusting the optical power oflenses while the passive devices have lenses constructed of spatiallyvarying optical power.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention, it beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set forth in the appendedclaims.

What is claimed is:
 1. A variable focus stereoscopic display systemmodifying a focus distance for viewing a stereoscopic display receivingimage data, the variable focus stereoscopic display system comprising: afirst lens positioned between a first eye and the stereoscopic display;a second lens positioned between a second eye and the stereoscopicdisplay; and wherein the first and second lenses are configured tomodify the optical power for the variable focus stereoscopic displaysystem and therefore the focus distance, the modification of the focusdistance comprising being based on a vergence of the first and secondeyes, changes in the focus distance are positively correlated withchanges in a convergence distance of lines of sight of the first andsecond eyes, and the changes in the focus distance are determinedindependently from the image data.
 2. The variable focus stereoscopicdisplay system of claim 1 further comprising: a sensor configured tosense an amount of the vergence; and a controller configured to modifythe optical power of the first and second lenses in response to theamount of the vergence.
 3. The variable focus stereoscopic displaysystem of claim 1 wherein each of the first and second lenses comprise:a first portion having a first optical power; and a second portionhaving a second optical power greater than the first optical power. 4.The variable focus stereoscopic display system of claim 3 wherein thefirst portions of the first and second lenses are adjacent to oneanother.
 5. The variable focus stereoscopic display system of claim 3wherein the first portions of the first and second lenses are offsetfrom the second portions with respect to a line between the first andsecond eyes.
 6. The variable focus stereoscopic display system of claim1 further comprising: a sensor configured to sense an amount of thevergence; a controller configured to modify the optical power of thefirst and second lenses in response to the amount of the vergence; athird lens positioned between the first eye and the stereoscopicdisplay; and a fourth lens positioned between the second eye and thestereoscopic display; wherein each of the third and fourth lensescomprise: a first portion having a first optical power; and a secondportion having a second optical power greater than the first opticalpower.
 7. The variable focus stereoscopic display system of claim 1further comprising: an apparatus configured to track a direction of agaze of the eyes and enable the variable focus stereoscopic displaysystem when the eyes are viewing the stereoscopic display and disablethe variable focus stereoscopic display system when the eyes are notviewing the stereoscopic display.
 8. The variable focus stereoscopicdisplay system of claim 1 wherein the first and second lenses arecalibrated to provide about a zero optical power at a viewer preferredfocus distance.
 9. The variable focus stereoscopic display system ofclaim 1 further comprising: a flight deck display system of an aircraftincluding the stereoscopic display.
 10. A method for adjusting a focusplane for viewing a stereoscopic display, comprising: sensing an amountof the vergence; altering a distance of the focus plane from first andsecond eyes in response to vergence of the first and second eyes,wherein changes in the focus plane distance are correlated with changesin the vergence such that the disparity between focus plane and aplurality of cues associated with the vergence are reduced from prior tothe distance being altered; modifying, in response to the amount of thevergence, an optical power of a first lens and a second lens positionedbetween the stereoscopic display and the first and second eyes,respectively; and generating image data to be displayed, whereingeneration of the image data is independent of the sensed amount ofvergence, and sensing the amount of vergence is independent of the imagedata.
 11. The method of claim 10 wherein the altering step compriseschanging the view of the stereoscopic display from a first portion ofeach of the first and second lenses to a second portion of each of thefirst and second lenses in response to a line of sight of the first andsecond eyes, the second portion having an optical power different thanthe first portion such that changes in the focus plane distance arepositively correlated with changes in a convergence distance associatedwith the cues.
 12. The method of claim 10 wherein the first and secondlenses comprise a single lens region.
 13. The method of claim 10 furthercomprising: tracking the direction of the gaze of the eyes; anddisabling the altering step when the first and second eyes are notviewing the stereoscopic display.
 14. The method of claim 13 furthercomprising: switching the focus plane to a nominal optical power settingwhen the altering step is disabled.
 15. The method of claim 13 furthercomprising: increasing the optical power as a convergence distanceassociated with the cues is decreased when the altering step isdisabled.